I do believe that if President Trump were to fire Robert Mueller we could see Republicans and Democrats alike moving toward impeachment. That is actually why I do not think it is likely he fires Mueller even though he clearly wants to.
Michael Cohen, a boil on the hemorrhoid on the butt of humanity, has had his office and hotel room raided by federal agents in search of documents related to porn star payments and other matters. This is far over the red line President Trump declared would be grounds for Mueller to be fired. For a long time there have been rumors that among the payments made by or on behalf of Trump were payments made to women who had had abortions. This is perhaps the one thing that could get evangelicals off the Trump wagon and anything related to that is now in the hands of federal prosecutors.
To go after Trump's lawyer, someone inside the Department of Justice would have had to convince a judge that fraud for a client was possible. As Cohen only really has one client, we can presume this is related to Donald Trump. The odds are that this is not about Russia, but about campaign finance issues that were never disclosed. The cover up is always what gets the big fish.
I do not expect to see impeachment on the immediate horizon. I think we are a ways from things wrapping up. I do think we will see more indictments of people around Donald Trump. And I do suspect Michael Cohen would squeal like a pig if threatened with jail time. A man that awful to others is typically awfully weak. This will get interesting.